UK growers must be allowed to continue applying economically optimum levels of fertiliser, especially nitrogen, to their crops.

And critics who claim that it damages the environment must justify it with sound scientific evidence.

Following the Danes in restricting inputs to below what offers the best return is not in the industry’s best interests.

That was the majority consensus among specialists at the event as discussions on revising DEFRA’s RB209 fertiliser recommendations book continued under growing EU pressure for the UK to abide by the EC Nitrates Directive.

Visitors’ views were being canvassed to ensure that the next RB209 avoided the sort of criticisms the current version had attracted – mainly that it was too prescriptive, was misleading on the impact of set-aside and ignored yield potential.

Publication of the eighth edition looked set to be delayed until next summer after a three-month DEFRA moratorium on funding, noted Peter Dampney of ADAS, one of the organisations involved in determining its content. “I hope that will continue to be based on the economic optimum.”

Reflecting environmental concerns, Danish growers had long been banned from applying more than 90% of the economic optimum, and that had recently been tightened to 85%, he noted.

Rothamsted Research’s Keith Goulding, who was encouraging as many people as possible to have their say on the way forward for RB209 via a questionnaire, believed that pursuing the Danish example without proof that the “economic optimum” risked damaging the environment would be wrong.

“It’s very hard to tell where the environmental optimum is,” added Prof Goulding. “Only at Rothamsted do we have the facility to show that.”

And that facility, the long-term experiment on Broadbalk Field, demonstrated that nitrate could still be lost from land even where no N fertiliser or manure had been applied since 1843, he pointed out.

However, Jane James of the Environmental Agency highlighted DEFRA’s Best Practice Survey which showed that a significant percentage of farmers still over-applied nitrogen – possibly as an insurance policy. And too few made proper allowance for the nutrients in livestock manures.

The EA claimed 80% of groundwater and 60-70% of rivers in the east of the country were at risk of eutrification [undesirable algal growths] which nitrogen encouraged.

The key to the new RB209 was that it should be credible, said colleague Jamie Letts. “We’re in the stakeholders’ group to decide how it should be produced. And we’ve asked for a section to be included on the environment.”

andrew.blake@rbi.co.uk